Preheat oven to 375 degrees F. Spray a 8x10-inch baking pan with nonstick cooking spray, set aside.
Heat oil in a large skillet over medium-high heat. Add potatoes, carrots, celery and onion. Sauté for 8-10 minutes, or until vegetables begin to soften.
Add garlic and season with salt and pepper. Mix in flour and chicken broth and let cook for 5 more minutes, stirring constantly.
Fold in peas and chicken and remove from heat. Mix in yogurt until well combined.
Spread mixture in an even layer in prepared pan.
Whisk together all crust ingredients until smooth and pour on top.
Bake, uncovered, for 45-50 minutes or until golden brown on top.